The present invention improves upon the loss characteristics of an optical waveguide and related measurement system of the kind described in U.S. patent application Ser. No. 10/868,475, filed Jun. 15, 2004, “Apparatus For Optical Measurements On Low-Index Non-Solid Materials Based On Arrow Waveguides”, which is hereby incorporated by reference in its entirety. This application was published on Dec. 16, 2004, with Publication Number US20040252957A1.